This invention relates to the use of a flash tank in an economizer cycle for a heat pump unit that is operable in both heating and cooling modes.
Usually, refrigerant heat pump systems provide cooled air in an air conditioning (cooling) mode and heated air in a heat pump (heating) mode. Essentially, the refrigerant flow through the system heat exchangers is reversed to provide the two distinct modes of operation.
One modern development in refrigerant cycles is the inclusion of a flash tank economizer cycle. In a flash tank economizer cycle refrigerant is partially expanded in the first expansion device downstream of a condenser, which is an outdoor heat exchanger in a cooling mode or an indoor heat exchanger in a heating mode, to some intermediate pressure and temperature and delivered to a flash tank, usually in a two-phase thermodynamic state. In a flash tank, which essentially is a refrigerant container, the refrigerant phase separation occurs. Refrigerant vapor is directed to an intermediate pressure port of the compressor (or in between the compressor stages, if the multi-stage compression is utilized) and refrigerant liquid is expanded once again in a second expansion device to the evaporation pressure (which is about equal to the pressure at the compressor suction port). The flash tank essentially acts as a 100% efficient economizer heat exchanger, where liquid and vapor refrigerant temperatures are equal to each other. Thus, refrigerant delivered to an evaporator, located downstream of the second expansion device, has lower vapor quality or higher liquid content, allowing for enhanced evaporator and overall system performance.
One challenge with regard to incorporating an economizer cycle into a refrigerant system that is utilized in both heating and cooling modes of operation is that distinct orifice sizes may be desirable for the expansion devices in the two modes. Thus, the applicant and the inventors of this application have previously developed a system wherein a distinct orifice is presented dependent on whether heating or cooling mode is being utilized for a heat pump system incorporating an economizer heat exchanger. This invention is disclosed in co-pending U.S. patent application Ser. No. 10,693,593, now U.S. Pat. No. 6,892,553, filed 24 Oct. 2003, and entitled “Combined Expansion Device and Four-Way Reversing Valve in Economized Heat Pumps.” It is desirable to provide similar arrangement for heat pump systems with the flash tank.
Another challenge for a refrigerant system designer is to reroute refrigerant flow through the system in such a way that the flash tank connection arrangement becomes independent from the position of the liquid refrigerant inlet and outlet ports and internal flash tank construction. Also, it would be desirable to provide such a schematic in a cost effective manner. Although economized heat pump systems with a flash tank are known to operate in either cooling or heating mode, it is highly desirable to extend such designs to the flash tank refrigerant systems operating in both modes to take advantages from the economized regime in both cases.